Method and Apparatus for Switching Between Edge Device Resources in an SDV System

ABSTRACT

A process is provided that may be employed by a set top terminal when a viewer is engaged in a SDV session and is required to switch from one edge device to another. The method begins when a set top terminal receives an SDV program forwarded over an access network by a first digital modulator. The SDV program is received on a first SDV channel associated with the first digital modulator. Next, a request is received to tune to a second SDV channel associated with a second digital modulator to thereby continue receiving the SDV program over the access network. The set top terminal detects an event indicating that a change from the first SDV channel to the second SDV channel will lessen disruption to a viewer of the SDV program. Finally, the set top terminal tunes to the second SDV channel.

FIELD OF THE INVENTION

The present invention relates generally to a switched digital videosystem for distributing content to a subscriber over a system such as asatellite or cable television system, and more particularly to aswitched digital video system that includes multiple edge deviceresources supplying content to the subscriber, which resources need tobe reallocated during a switched digital video session in which thesubscriber is viewing the content.

BACKGROUND OF THE INVENTION

Switched digital video (SDV) refers to an arrangement in which broadcastchannels are only switched onto the network when they are requested byone or more subscribers, thereby allowing system operators to savebandwidth over their distribution network. In conventional cable orsatellite broadcast systems, every broadcast channel is always availableto all authorized subscribers. In contrast, a switched digital videochannel is only available when requested by one or more authorizedsubscribers. Also, unlike video on-demand, which switches a singlecastinteractive program to a user, switched digital video switches broadcaststreams, making each stream available to one or more subscribers whosimply join the broadcast stream just as they would with normalbroadcast services. That is, once a switched service is streamed to asubscriber, subsequent subscribers associated with the same servicegroup as the first subscriber can tune to the same broadcast stream. Theswitched digital video will often share the same resource managers andunderlying resources with other on demand services.

As noted, switched digital video is largely a tool to save bandwidth.From the subscriber perspective, he or she still receives the samebroadcast video service when using a switched broadcast technique;ideally the user is not able to discern that the stream was switched atall. If each one of the digital broadcast channels is being watched bysubscribers in the same service group, the switched digital videoapproach does not yield any bandwidth savings. However, a more likelysituation statistically is that only a certain number of the digitalbroadcast channels are being watched by subscribers in the same servicegroup at any given time. Those channels not requested by a subscriberneed not be broadcast, thereby saving bandwidth.

One way to support switched digital video is to utilize the SessionManager to manage broadcast sessions. For each channel change, thesubscriber will set up a broadcast session with the Session Manager,which will determine if the requested channel is already being sent tothe corresponding service group that the subscriber belongs to. Thesubscriber will be assigned to join the existing broadcast session ifthe requested channel is available at the service group or assigned to anew broadcast session if the requested channel is not available at theservice group. The Session Manager will negotiate with the ResourceManagers to allocate resources required for the session. The edge device(e.g., a digital modulator such as a QAM modulator) needs to dynamicallyretrieve the MPEG single program transport stream that carries therequested broadcast program (likely via IP multicast) and generate theMPEG multiple program transport stream. As part of the session setupresponse message, the video tuning parameters such as frequency and MPEGprogram number are sent back to the subscriber to access the requestedbroadcast channel.

For purposes of managing the resources of the edge devices, it maysometimes be important to move viewers from one edge device to anothereven during a SDV session. Unfortunately, this can be disruptive to theviewer because there can be a short delay (e.g., a few seconds) whilethe switch to the new edge device is performed.

Accordingly, it would be desirable to provide a method and apparatus forswitching a set top terminal during an SDV session from receiving aprogram on one edge device to receiving the program on another edgedevice with minimal viewer impact. This would allow the SDV system tobetter manage the resources of its edge devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example of a system architecture for deliveringswitched digital video content to a subscriber.

FIG. 2 shows one example of headend 110.

FIG. 3 shows one example of a set top terminal.

FIG. 4 shows a LAN over which two set top terminals communicate.

FIG. 5 is a flowchart showing one example of a process that may beemployed by a set top terminal when a viewer is engaged in a SDV sessionand is required to switch from one edge device to another.

FIG. 6 shows an example of a set top terminal that includes two tuners.

FIG. 7 is a flowchart showing another example of a process that may beemployed by a set top terminal when a viewer is engaged in a SDV sessionand is required to switch from one edge device to another.

DETAILED DESCRIPTION

FIG. 1 is a system architecture 100 for delivering switched digitalchannels to a subscriber during a switched digital video (SDV) session.The SDV session is implemented through a service offering in whichapplication level data generated by a set-top terminal initiates a SDVsession request and an SDV manager routes data in accordance with therequest to provision the service. Among other components, systemarchitecture 100 comprises a content source such as a headend 110 thatis connected to multiple intermediate entities such as hubs 130, 132 and134. The headend 110 communicates with a switch or router 170 in hubs130, 132 and 134 over links L1, L2 and L3, respectively. The headend 110and hubs 130, 132 and 134 may communicate over a packet-switched networksuch as a cable data network, passive optical network (PON) or the likeusing, for example, IP multicast addressing.

Some or even all of the hubs are connected to multiple users, typicallyvia distribution networks such as local cable access networks (e.g., HFCnetworks). For simplicity of explanation only, each hub is shown asbeing connected to a distinct HFC network, which in turn communicatewith end user equipment as illustrated. In particular hubs 130, 132 and134 in FIG. 1 communicate with access networks 140, 142 and 144,respectively. Each access network 140, 142 and 144 in turn communicateswith multiple end user devices such as set top terminals. In the exampleof FIG. 1, access network 140 communicates with set top terminals 120 ₁,120 ₂, 120 ₃, 120 ₄ and 120 ₅, access network 142 communicates with settop terminals 122 ₁, 122 ₂, 122 ₃, 122 ₄, and access network 144communicates with set top terminals 124 ₁, 124 ₂, 124 ₃.

In addition to the switch or router 170, each hub can include an arrayof radio frequency transmitter edge devices such as edge QAM modulators150. The number of edge devices 150 in each hub may vary as needsdictate. As used herein, the term “QAM” refers to modulation schemesused for sending signals over cable access networks. Such modulationschemes might use any constellation level (e.g. QAM-16, QAM-64, QAM-256etc.) depending on the details of a cable access network. A QAM may alsorefer to a physical channel modulated according to such schemes.Typically, a single QAM modulator can output a multiplex of ten ortwelve programs, although the actual number will be dictated by a numberof factors, including the communication standard that is employed. Theedge QAM modulators usually are adapted to: (i) receive Ethernet framesthat encapsulate the transport packets, (ii) de-capsulate these framesand remove network jitter, and (iii) transmit radio frequency signalsrepresentative of the transport stream packets to end users, over theHFC network. Each transport stream is mapped to a downstream QAMchannel. Each QAM channel has a carrier frequency that differs from thecarrier frequency of the other channels. The transport streams aremapped according to a channel plan designed by the MSO that operates thenetwork.

Each hub 130, 132 and 134 also includes an edge resource manager 160 forallocating and managing the resources of the edge devices 150. The edgeresource manager 160 communicates with and receives instructions fromthe session manager located in the headend 110.

FIG. 2 shows one example of headend 110. The headend 110 includes abroadcast content source 210, which may include, by way of example,satellite receivers, off-air receivers and/or content storage devicessuch as servers. A SDV manager 215 is used to determine which SDVtransport streams are active at any time and for directing the set topterminals to the appropriate stream. The SDV manager 215 also keepstrack of which subscribers are watching which channels and itcommunicates with the edge resource managers 160 in the hubs so that thecontent can be switched on and off under the control of the SDV manager215. In addition, all subscriber requests for a switched digital channelgo through the SDV manager 215. The switched digital channels areforwarded to a rate clamp 220 and one or more encryptors 225 using, forexample, IP multicast addressing. The content is then encrypted by theencryptors 225 and transmitted to the appropriate hub or hubs.Typically, standard definition (SD) channels are currently rate clampedto 3.75 Mbps while high definition channels are currently rate clampedto between about 12 Mbps and 15 Mbps. The encryptors 225 encrypt thedigitally encoded content, often under the control of a conditionalaccess system (not shown).

Headend 110 may also include a network DVR 240. The network DVR 240stores content that can be transmitted to set top terminal via a hub andaccess network in response to a user request to play a program stored onthe DVR 240. Other user input requests are also serviced by network DVR240, including, for example, requests to accelerate the playing of aprogram in the forward direction (e.g., cueing) and in the reversedirection (e.g., reviewing). The content is stored by the network DVR240 upon a user request. The content may be provided to the network DVR240 from any available content source, including, for example, contentsource 210.

Headend 110 may also include a variety of other components for offeringadditional services. For example, in FIG. 2 a video on demand (VOD)server 230 is shown for storing programs or other content fordistribution to subscribers on an on-demand basis. Although not shown,one of ordinary skill in the art would recognize that other componentsand arrangements for achieving the various functionalities of headend110 are possible. For example, the head-end 110 may comprise typicalhead-end components and services including a billing module, anadvertising insertion module, a subscriber management system (SMS), aconditional access system and a LAN(s) for placing the variouscomponents in data communication with one another. It will also beappreciated that the head-end configuration depicted in FIG. 2 is ahigh-level, conceptual architecture and that each network may havemultiple head-ends deployed using different architectures.

One example of a set top terminal 300 is shown in more detail in FIG. 3.It should be noted that set top terminal 300 more generally may be anyapparatus such as a hardware card, specially programmed computer orother device having the functionality described herein that may beplaced near to or within a television or other display device (such as acomputer monitor) such as display unit 270. The set top terminal 300receives content from cable access networks seen in FIG. 1. Broadlyspeaking, a traditional set top terminal such as that depicted in FIG. 3is a device that can receive, store and forward content withoutmanipulating the content in any significant way except to format it sothat it may be rendered in a suitable manner.

Set-top terminal 300 includes an in-band tuner 302, which tunes to achannel signal selected by a consumer (not shown) via user interface304. User interface 304 may be any control device such as a remotecontrol, mouse, microphone, keyboard, or display. NTSC demodulator 340and digital demodulator 342 are responsive to in-band tuner 302. NTSCdemodulator 340 includes components responsive to receive analogversions of a channel signal. A digital demodulator 342, which as shownis a QAM demodulator, but, which may be any type of digital demodulatordevice, includes components responsive to receive digital versions of achannel signal, and to output video information. QAM demodulator 342receives and processes digital data packets from one or more digitalsources, such as a digital television signal, an MPEG transport stream,or a media stream from an external network connection, such as cablemodem 315 (if available), using well-known methods and techniques. Videodecoder 344 is responsive to receive and decode video information. Videoinformation that may require format translation or modification forcompatibility with capabilities of set top terminal 300 may be passed toencoder 341 for formatting. Video information that is in a formatpreferred for use by MPEG Decoder/Multi Media Processor 349 may bepassed directly to MPEG Decoder/Multi Media Processor 349. Encoder 341is operative to perform predetermined coding techniques (for example,MPEG-2, MPEG-4, and others) to produce an encoded video signal fortransmission to MPEG Decoder/Multi Media Processor 349, or for storage.MPEG Decoder/Multi-Media Processor 349 is operative to performpredetermined coding techniques to arrange video information intodisplayable formats, in accordance with well-known methods andtechniques. Internal arrangements of MPEG Decoder/Multi-Media Processor349 are well known, and may include analog-to-digital converters, one ormore storage media and/or buffers, and general or special-purposeprocessors or application-specific integrated circuits, along withdemultiplexers for demultiplexing and/or synchronizing at least twotransport streams (for example, video and audio).

An electronic program guide (EPG) 355 is also provided in set-topterminal 300. The EPG 355 is an interactive, on-screen display featurethat displays information analogous to TV listings found in localnewspapers or other print media. An EPG provides information about eachprogram being broadcast within the time period covered by the EPG, whichtypically ranges from the next hour up to several days. The informationcontained in an EPG includes programming characteristics such as, forexample, channel number, program title, start time, end time, elapsedtime, time remaining, a brief description of the program's content andpossibly the names of individuals associated with the program such asthe actors, writers and director. The EPG, which is generally receivedalong with the programming content, may be updated on a periodic basisso that the consumer can make appropriate selection for upcomingprograms. For example, the electronic program guide 355 may displayprograms in a tabular format by channel and time so that the user canmake selections of desired content. In some cases, instead oftransmitting it along with the programming, the electronic program guide355 may be downloaded via a telephone line, cable connection, satelliteup-link, or radio broadcast antenna.

An on-screen display unit 350 is provided in set top terminal 300. Theon-screen display unit 350 is used to display information such ascontrol menus and the like as well as information received from theservice provider or MSO that needs to be directly presented to the userregardless of the particular programming or channel that the user iscurrently viewing. In particular, on-screen display unit 350 displaysthe information provided by the EPG 355. Accordingly, on-screen displayunit 350 can forward the information directly to the display unit 270,where it may appear as an overlay, pop up, or scrolling text ticker thatis superimposed on the current programming being viewed. Alternatively,the information from the on-screen display unit 350 may even replace thecurrent programming that appears on the display unit 270.

DVR subsystem 360 is provided for recording programs received from theaccess network. DVR subsystem 360 can control the channel tuned by tuner302 and record programming on a manual or timer control basis.Additionally, the DVR subsystem 360 can buffer incoming programs toenable a view to pause or replay a portion of a live program.

Set-top terminal 300 further includes a computer-readable storage medium306. Computer-readable storage medium 306 may be any local or remotedevice capable of recording or storing data, and in particular may be,or may include, a read only memory (“ROM”), flash memory, random accessmemory, a hard disk drive, all types of compact disks and digitalvideodisks, and/or magnetic tape. Various application programs mayreside on storage medium 306. The applications residing on storagemedium 306 may be computer programs that include software componentsimplemented according to well-known software engineering practices forcomponent-based software development and stored in computer-readablememories, such as storage medium 306. The applications, however, may beany signal processing methods and/or stored instructions, in one or moreparts, that electronically control functions set forth herein. Storagemedium 306 may also include other programs to provide additionalfunctionality. For example, a network interface program 308 may beprovided that represents aspects of the functional arrangement ofvarious computer programs that pertain to the receipt and processing ofcontent and other data over the broadband system 100.

In some implementations the set top terminal 300 includes a clock (notshown) that may be periodically synchronized with a clock signalreceived from the headend or which may be synchronized by other means.

The various components of set top terminal 300 discussed above may alloperate under the overall control of a processor 365. Moreover, it iscontemplated that the processor 365, tuner 302, MPEG Decoder/Processor349, user interface 304, onscreen display unit 350 and the othercomponents shown in FIG. 3 may each be implemented in hardware, softwareor a combination thereof. In addition, although the various componentsare shown as separate processors, it is contemplated that they may becombined and implemented as separate processes on one or moreprocessors.

When a viewer selects an SDV channel using a set top terminal, the SDVsystem actively switches the channel onto one of the QAMs that servesthat particular set top terminal. The set top terminals are generallyarranged into service groups and each of the service groups is assignedto, and serviced by, one or more QAM modulators. For example, in thearrangement depicted in FIG. 1 set top terminals 120 ₁, 120 ₂, 120 ₃,120 ₄ and 120 ₅ are assigned to QAM modulators 150 located at hub 130,set top terminals 122 ₁, 122 ₂, 122 ₃, 122 ₄ are assigned to QAMmodulators 150 located at hub 132, and set top terminals 124 ₁, 124 ₂,124 ₃ are assigned to QAM modulators 150 located at hub 134. Typically,four (4) or eight (8) QAM modulators are deployed per service group tocarry the SDV channels. SDV service groups currently include from about500 to 1000 set top terminals. Depending on the system topology, theremay or may not be a one-to-one correspondence between the hubs and theservice groups. For instance, it is typically the case that each hubserves multiple service groups.

Once a set top terminal is tuned to a channel on a particular QAMmodulator, it is difficult to switch the viewer to a different modulatorsince the time needed to accomplish the re-tuning process may impact theviewer experience. Forcing the set top terminal to switch from one QAMmodulator to another will typically result in the loss of 2-3 seconds ofchannel viewing because of various delays, including, for example,delays caused by tuning to the new QAM modulator, acquiring an I-frame,if necessary, and the like.

Despite this problem there are several reasons it may be desirable ornecessary to move viewers from one QAM modulator to another. Forexample, a QAM modulator may need to be taken down for maintenancepurposes. In another example, multiple copies of the same SDV channelmay be being delivered to the same service group (using differentencoding rates, changing multicast sources, switched broadcast versusswitched narrowcast, etc.) and the SDV system may wish to consolidatethe viewers onto a single QAM to conserve bandwidth. As another example,because different QAM modulators may serve different sized regions(switched broadcast versus switched narrowcast), the SDV system may needto move an SDV channel between QAM modulators to achieve greaterefficiencies.

A variety of approaches may be employed to reduce the impact on thesubscriber arising from the need to switch to a different QAM modulatorduring a SDV session. For example, in one approach, the QAM modulatorscan be switched during a transition from a program to a commercial orduring transitions between commercials. The timing of such transitionscan be determined by consulting the program listings and scheduledadvertising, which can be provided to the set top terminal by the SDVmanager 215 along with the request to change from one QAM modulator toanother. Alternatively, headend 110 can provide a clock signal to theset top terminal indicating when commercials are scheduled. The set topterminal can compare the clock signal to the time indicated by its owninternal clock to determine the arrival of the commercials.

In yet another alternative, the commercial transitions can be determinedby the set top terminal itself since a black screen is generallyinserted into the video stream between commercials and between a programand commercials. In this case, upon receiving a signal from the SDVmanager 215 to change from one QAM modulator to another, the set-topterminal can wait to make the change until it detects the black screen(by, for example, scanning the decoded image), at which point theprocessor 365 can direct the tuner 302 to tune to the new modulator. Theoriginal QAM modulator can be notified by the set top terminal when ithas made the transition to the new QAM modulator so that the originalQAM modulator can stop transmitting the SDV program. Alternatively, theSDV manager 215 can notify the set top terminal that the SDV programwill be terminated on the original QAM modulator in some specifiedperiod of time (e.g., 15 minutes). In this case the set top terminalwill need to transition to the new QAM modulator within this specifiedperiod of time. Although in all these various cases the viewer willstill experience a 2-3 second interruption as the transition is made,its impact on the viewing experience is minimized since the retuneprocess occurred at a boundary with a commercial.

In another approach, after receiving a request to change from one edgeQAM modulator to another, the processor 365 can direct the tuner 302 totune to the new modulator when a viewer displays the electronic programguide (EPG) using the user interface. When the program listings aredisplayed, the current channel is usually not visible on the displayunit. The set top terminal thus can retune to the new edge QAM modulatorwithout any viewing impact. Alternatively, in some cases the EPG maydisplay a thumb nail of the current channel. In this case the set topterminal can retune to the new QAM modulator before displaying the thumbnail. The viewer is not likely to notice the retune since it can beperformed while the EPG initializes the display. If the EPG finishesupdating the display before the retune operation completes, however, theprocessor can instruct the on-screen display unit 350 to display eithera black box in place of the thumb nail, advertising, or the last imageof the SDV channel before the retune started.

As shown in FIG. 6, many set top terminals are supplied with two or moretuners (e.g., tuners 302 and 303)) so that, for example, one program canbe recorded while another program is being watched. In FIGS. 3 and 6,like elements numerals are denoted by like reference numerals. Such settop terminals can be used to reduce the impact on the subscriber whenswitching from one QAM modulator to another during a SDV session. Inparticular, if the second tuner is not being used for recording orviewing a second channel, the set top terminal can be instructed byprocessor 365 to tune to the new QAM on the second tuner. When the tuneoperation completes, the set top can swap tuners that feed the displayunit 270. Once the swap is complete, the set top terminal can tune offthe first QAM modulator. In some cases, to minimize interruptions, theswap could occur either during a black frame (transition betweentelevised program and advertisement) or when a new I-Frame is received.

In another approach, the network DVR 240 shown in FIG. 2 can be usedwhen switching from one edge device to another. When a set top terminalis instructed by the SDV manager 215 to switch to a new QAM modulator,the processor 365 in the set top terminal 150 can “pause” the currentstream, thus continuing to display the last frame or image before thestream was paused. While pausing the last frame from the current QAMmodulator, the SDV system begins to transmit the same frame on the newQAM modulator as many times as necessary until the retune operationcompletes. During this process, the network DVR system records the SDVchannel so that none of the content is lost while retuning is performed.When the re-tune operation completes, the SDV system begins playing theprogram recorded by the network DVR 240 with the frame immediatelyfollowing the frame that was paused. That is, the network DVR will beginplaying the program a few seconds after it has been initially broadcastover the SDV channel. Thus, although there was an interruption of 2-3seconds, the viewer will not miss any of the program. If the viewer wereto switch off the SDV channel and then return to it at a subsequentpoint in time, the SDV system may present the subscriber with thecurrent stream rather than the program recorded by the network DVR 240.

In some cases a residence or other premises has more than one televisionor other display, each of which requires their own set top terminal. Forinstance, televisions are often located in living rooms, bedrooms andkitchens. More and more such set top terminals are being networkedtogether so that they can communicate with one another and shareinformation so that, for instance, a program recorded by the DVR in oneset top terminal can be played on a television associated with anotherset top terminal. Because all these devices are networked, they canshare network resources. For example, an unused networked set topterminal with a DVR that resides in a bedroom can be used when switchingfrom one edge device to another to minimize viewer disruption.

As shown in FIG. 4 set top terminals 410 and 420 located in a singleresidence or building may communicate with one another over a LAN 430that operates in accordance with any of a variety of differentcommunication standards such as Ethernet, Powerline Communication (PCL)networks, MoCA (Multimedia over Coax Alliance) and certain wirelessmechanisms (e.g., 802.11, Bluetooth), which allow connectivity betweendifferent networked devices such as televisions, media centers, set topterminals, digital video recorders, stereos, computers, and appliances.The standards may be implemented in a wireless or wired manner using,for example, already installed coax cable.

If one of the set top terminals 410 and 420 that communicate over theLAN 430 includes a DVR, their tuners can be used to prevent or minimizeviewer disruption of a program during a switch from one edge device toanother. In the example of FIG. 4 set top terminal 420 is assumed toinclude a DVR 425. On the other hand, set top terminal 410 may or maynot include a DVR. When the set top terminal 410 and 420 initiallyregister with the SDV manager 215, their capabilities, including theirstatus on the same LAN, is communicated to the SDV manager 215. In thisway the SDV manager 215 can oversee and coordinate the following processin which the set top terminal 420 effectively serves as a proxy for theset top terminal 410 while the transition from one QAM modulator toanother is performed. In this case, when the set top terminal 410 isbeing used in an SDV session and is instructed by the SDV manager 215 toswitch to a new QAM modulator, the processor in the set top terminal410, under the control of the SDV manager 215, can “pause” the currentstream, thus continuing to display the last frame or image before thestream was paused. During this process, the second set top terminal 420,which is equipped with the DVR 425, is instructed to tune to the SDVchannel on which the program is being supplied by the new QAM modulatorso that none of the content is lost while retuning is performed. Whenthe re-tune operation completes, the first set top terminal 410 on whichthe program is being viewed receives the program from the DVR 425 in thesecond set top terminal 420 over the LAN 430. Similar to the case inwhich a network DVR is employed, the DVR 425 in the second set topterminal 420 begins playing the program with the frame immediatelyfollowing the frame that was paused. That is, the DVR 425 will beginplaying the program a few seconds after it has been initially broadcastover the SDV channel of the new QAM modulator. Thus, although there wasan interruption of 2-3 seconds, the viewer will not miss any of theprogram.

FIG. 5 is a flowchart showing one example of a process that may beemployed by a set top terminal when a viewer is engaged in a SDV sessionand is required to switch from one edge device to another. The methodbegins in step 510 when the set top terminal receives an SDV programforwarded over an access network by a first digital modulator such asQAM modulator. The SDV is received on a first SDV channel associatedwith the first digital modulator. At some point while the program isbeing viewed, the set top terminal receives a request from the SDVmanager in step 520 instructing it to tune to a second SDV channelassociated with a second digital modulator so that it can continuereceiving the SDV program over the access network. In step 530, the SDVmanager instructs the set top terminal to pause the SDV program receivedon the first SDV channel so that a current image of the program iscontinuously displayed. Next, in step 540, the SDV manager alsoinstructs the set top terminal to tune to the second SDV channel afterpausing the SDV program. Finally, in step 550, a delayed rendition ofthe SDV program is provided to the set top terminal, beginning with thecurrent image of the program. In this way viewer will not miss any ofthe program as a result of the switch from one digital modulator toanother. The delayed rendition of the SDV program may be received overthe access network on the second SDV channel from a network-based DVR.Alternatively, the delayed rendition of the SDV program may be receivedby the set top terminal over a LAN from a DVR that itself has receivedthe delayed rendition over the access network on the second SDV channel.

FIG. 7 is a flowchart showing another example of a process that may beemployed by a set top terminal when a viewer is engaged in a SDV sessionand is required to switch from one edge device to another. The methodbegins in step 710 when a set top terminal receives an SDV programforwarded over an access network by a first digital modulator. The SDVprogram is received on a first SDV channel associated with the firstdigital modulator. Next, in step 720, a request is received to tune to asecond SDV channel associated with a second digital modulator to therebycontinue receiving the SDV program over the access network. The set topterminal detects an event in step 730. The event indicates that a changefrom the first SDV channel to the second SDV channel will lessendisruption to a viewer of the SDV program. Finally, in step 740, the settop terminal tunes to the second SDV channel.

The processes described above, including but not limited to thosepresented in connection with the headend and set-top terminal may beimplemented in general, multi-purpose or single purpose processors. Sucha processor will execute instructions, either at the assembly, compiledor machine-level, to perform that process. Those instructions can bewritten by one of ordinary skill in the art following the description ofpresented above and stored or transmitted on a computer readable medium.The instructions may also be created using source code or any otherknown computer-aided design tool. A computer readable medium may be anymedium capable of carrying those instructions and include a CD-ROM, DVD,magnetic or other optical disc, tape, silicon memory (e.g., removable,non-removable, volatile or non-volatile), packetized or non-packetizedwireline or wireless transmission signals.

1. At least one computer-readable medium encoded with instructionswhich, when executed by a processor, performs a method including:receiving an SDV program forwarded over an access network by a firstdigital modulator, said SDV program being received on a first SDVchannel associated with the first digital modulator; receiving a requestto tune to a second SDV channel associated with a second digitalmodulator to thereby continue receiving the SDV program over the accessnetwork; detecting an event indicating that a change from the first SDVchannel to the second SDV channel will lessen disruption to a viewer ofthe SDV program; and tuning to the second SDV channel.
 2. The computerreadable medium of claim 1 wherein the SDV program is received in aquadrature amplitude modulated (QAM) signal.
 3. The computer readablemedium of claim 1 wherein the event that is detected is a clock valueindicating that a transition is scheduled from the SDV program to acommercial or from one commercial to another commercial.
 4. The computerreadable medium of claim 3 wherein the clock value is scheduled isreceived over the access network.
 5. The computer readable medium ofclaim 1 wherein the event that is detected is a transition from the SDVprogram to a commercial or from one commercial to another commercial. 6.The computer readable medium of claim 5 wherein the transition isdetected using black screen detection.
 7. The computer readable mediumof claim 1 wherein the event that is detected is a viewer commandrequesting an EPG to be displayed.
 8. The computer readable medium ofclaim 1 further comprising: tuning to the second SDV channel whilecontinuing to receive the SDV channel on the first SDV channel;displaying the SDV program received on the second SDV channel;terminating receipt of the SDV program received on the first SDV channelafter initiating display of the SDV program received on the second SDVchannel.
 9. The computer readable medium of claim 8 wherein the eventthat is detected is an availability of a second tuner to receive the SDVchannel on the second SDV channel.
 10. At least one computer-readablemedium encoded with instructions which, when executed by a processor,performs a method including: receiving an SDV program forwarded over anaccess network by a first digital modulator, said SDV program beingreceived on a first SDV channel associated with the first digitalmodulator; receiving a request to tune to a second SDV channelassociated with a second digital modulator to thereby continue receivingthe SDV program over the access network; pausing the SDV programreceived on the first SDV channel so that a current image of the programis continuously displayed; tuning to the second SDV channel afterpausing the SDV program; receiving and displaying a delayed rendition ofthe SDV program beginning with the current image of the program.
 11. Thecomputer readable medium of claim 10 wherein the delayed rendition ofthe SDV program is received over the access network on the second SDVchannel.
 12. The computer readable medium of claim 11 wherein thedelayed rendition of the SDV program is provided by a network-based DVR.13. The computer readable medium of claim 10 wherein the delayedrendition of the SDV program is received over a LAN from a DVR that hasreceived the delayed rendition over the access network on the second SDVchannel.
 14. The computer readable medium of claim 10 wherein tuning tothe second SDV channel occurs upon detection of an event.
 15. Thecomputer readable medium of claim 14 wherein the event is a transitionfrom the SDV program to a commercial or from one commercial to anothercommercial.
 16. The computer readable medium of claim 10 wherein thedelayed rendition of the SDV program is delayed by about an amount oftime needed to tune from the first SDV channel to the second SDVchannel.
 17. A switched digital video (SDV) system, comprising: a SDVmanager for coordinating a SDV session requested by a subscriberterminal; an input receiving content to be broadcast during the SDVsession; a plurality of edge devices for receiving a transport streamthat includes broadcast content provided by the content source andtransmitting the transport stream over an access network to thesubscriber terminal on one of a plurality of SDV channels; and whereinthe SDV manager is configured to (i) request a first of the edge devicesto transmit selected broadcast content to the subscriber terminal over afirst SDV channel and (ii) terminate, at a subsequent time, transmissionof the selected broadcast content over the first SDV channel and insteadrequest a second of the edge devices to transmit a delayed rendition ofthe selected broadcast content to the subscriber terminal over a secondSDV channel.
 18. The SDV system of claim 17 further comprising anetwork-based DVR for receiving the selected broadcast content from theinput and providing the delayed rendition of the selected broadcastcontent.
 19. The SDV system of claim 17 wherein the SDV manager isfurther configured to instruct the subscriber terminal to (iii) pausethe selected broadcast content received on the first SDV channel and(iv) tune to the second SDV manager.